1. Field of the Invention
The present invention relates to a spindle motor and a recoding disk driving device including the same.
2. Description of the Related Art
Generally, a small spindle motor used in a hard disk drive (HDD) serves to rotate a disk so that a magnetic head may write data to the disk or read data from the disk.
In addition, the spindle motor is provided with a hydrodynamic bearing assembly, and a bearing clearance formed in the hydrodynamic bearing assembly is filled with a lubricating fluid.
In addition, during rotation of a shaft, the lubricating fluid filled in the bearing clearance is pumped to form fluid dynamic pressure therein, thereby rotatably supporting the shaft.
However, pressure lower than atmospheric pressure, that is, negative pressure, may be generated in the bearing clearance due to the pumping of the lubricating fluid during rotation of the shaft.
In this case, air contained in the lubricating fluid expands, such that air bubbles may be formed. When such air bubbles are introduced into a groove pumping the lubricating fluid, deterioration of rotational characteristics such as the generation of insufficient fluid dynamic pressure, the generation of vibrations, and the like, is caused.
Therefore, a circulation hole for decreasing the generation of negative pressure is formed in a sleeve to suppress the generation of negative pressure.
In the following Related Art Document (US 2009-80819), a configuration in which a circulation hole for decreasing the generation of negative pressure is formed to be inclined and connects a bearing clearance formed by a sleeve and a cover member and a bearing clearance in which a liquid-vapor interface is formed to each other has been used.
However, it may be relatively difficult to process the circulation hole and a defect of the sleeve may occur during processing of the circulation hole.
Further, recently, durability, that is, durability allowing for a longer lifespan of the spindle motor, has been demanded in spindle motors. In addition, in order to increase the lifespan of spindle motors, the bearing clearance should be sufficiently filled with lubricating fluid, and the spindle motor should be operated normally, even in the case that a predetermined amount of lubricating fluid has evaporated.
That is, the development of a structure allowing the spindle motor normally operated, even in the case that a predetermined amount of lubricating fluid is evaporated, has been demanded.